Hyperthermia or induced high body temperature has been considered beneficial in treating various human diseases including many types of cancer. More specifically, various types of malignant growths are considered by many researchers to have a relatively narrow hyperthermia treatment temperature range. Below a threshold temperature of about 41.5 degrees Celsius, thermal destruction of these malignancies is not possible, and in fact their growth may be stimulated. However, at temperatures above a range of about 43 to 45 degrees Celsius thermal damage to most normal body tissue cells occurs if exposure lasts for even a relatively short duration.
While some types of skin cancers are known to respond to direct application of surface heat, deeply located malignant growths, owing to normal blood flow body heat transfer properties of the body, were most difficult to heat to the desired temperature without damaging overlying healthy tissue. A solution to this problem has been the development of electromagnetic radiation (EMR) heating devices for inducing hyperthermia. This form of treatment is known as "diathermia".
EMR heating of subsurface growths from an exterior surface is ordinarily enabled by configuration and placement of one or more applicators and by appropriate selection of EMR frequency, phase and intensity. Nevertheless, tissue growths inside of, or in close proximity to, heat sensitive tissue or organs, are much more effectively and safely heated by EMR irradiating applicators positioned within the body as closely as possible to the growth requiring treatment.
The advantages of positioning EMR applicators relatively close to the growth to be heated by radiation include improved heating control, more localized heating and consequently less possibility of overheating adjacent healthy tissue and more direct treatment of the enlarged tissues causing the undesireable symptoms.
Close applicator access to certain types of diseased tissue growths is provided by surgical procedures for naturally occurring body passages such as the esophagus, larynx, prostate gland and colon. Surgical procedures enlarge the passage by cutting away the passage tissue. Some heating methods are placing over the tissue or in an incision small EMR applicators to provide direct irradiation of the growth. An illustrative type of a body passage insertable EMR applicator is described in U.S. Pat. No. 2,407,690 issued to Southworth. The Southworth type body passage EMR applicators have been configured in a manner causing a heating pattern that tends to be concentrated at the radiating tip of the applicator and which decreases at a usually exponential rate from such tip towards the radiation source.
Special and difficult problems often attend growths found along natural body passages. For example, diseased tissue tends to spread around and along the passage, often in a relatively thin layer Typically, the diseased layer may be less than a centimeter thick and may extend as far as 6-10 centimeters along the passage. The use of Southworth type applicators result in nonuniform irradiation heating of the elongated growth. Thus, the temperature at the tip may have to be so hot that it kills surrounding healthy tissue in order to make the tip towards the power supply hot enough to kill the growth.
Ridged and nonflexible antenna rectal inserted devices are known. Examples of such devices are disclosed in U.S. Pat. No. 4,601,296 issued to Yerushalmi, and a 1980 article titled "Microwave Applicators for Localized Hyperthermia Treatment of Cancer of the Prostate" by Mendecki et al., Int. J. Radiation Oncology, Biol. Phys., Vol. 6, pp. 1583 and 1588.
Also, helical coil designs have been used to heat tissues placed within the cylindrical opening of the device. Such devices are disclosed in U.S. Pat. No. 4,527,550 issued July 1985 to Ruggera.
A body passage insertable applicator apparatus for EMR systems is known that includes a urethral inserted probe having a monopole antenna (Microwave Surgical Treatment of Diseases of Prostate, Harada et al., Urology, December 1985, Vol. XXVI, No. 6, pp. 572-576). Also known is a helical wound coil applicator having coaxial inner and outer conductors electrically connected at an EMR input end to a conventional coaxial transmission line for transmitting high frequency EMR from a source to the applicator. The applicator outer conductor is longitudinally split on opposite sides to form first and second outer conductor segments. The inner conductor is electrically connected to an applicator termination end of one of such segments. A dielectric media is disposed between the applicator inner and outer conductors, and the outer conductor and termination end are covered by a dielectric sheath. A substantially uniform, external electric tissue heating field is obtained along substantially the entire length of the applicator by exponentially increasing the thickness of the dielectric sheath towards the termination end and making the thickness of the sheath over the termination end equal to at least half the outer diameter of the applicator. Those persons skilled in the art desiring further information concerning this device are referred to U.S. Pat. No. 4,658,836 issued Apr. 21, 1987 to Paul F. Turner.
A principal feature distinguishing the present invention from the prior art devices is the provision of urethral insertable EMR applicator principally adapted for benign prostatic hyperplasia (BPH), which provides the generally cylindrical or longitudinally uniform EMR heating pattern necessary to enable substantially uniform heating of BPH growths or other tissue diseases associated with the urinary track.